1. Field of the Invention
The present invention relates to a lens and a method for producing such a lens.
2. Description of the Related Art
To correct chromatic aberration in optical systems such as cameras, a plurality of lenses have been used. In particular, optical systems used under white light sources require a large number of lenses for correcting chromatic aberration. However, when chromatic aberration is corrected with a radial gradient index lens having a refractive index distribution in the radial direction with respect to the optical axis, the number of lenses for correcting chromatic aberration can be decreased and the size of zoom lenses can be reduced.
There is a lens having a refractive index distribution in which the lens is composed of polymers formed from two organic monomers having different refractive indices and the refractive index distribution is formed by a three-dimensional distribution of the concentration proportions of the polymers (Japanese Patent Laid-Open No. 8-244130).
Variation in the performance of optical devices such as lenses according to change in the environment such as temperature change is desirably small. In particular, variation in the shape of lenses causes variation in the focal length, which is problematic. In general, an indicator of variation in the shape of a material according to temperature change is a thermal expansion coefficient (ppm/K). Optical devices such as lenses desirably have a low thermal expansion coefficient.
The lens having a refractive index distribution in Japanese Patent Laid-Open No. 8-244130 is formed from organic monomers and hence has a high thermal expansion coefficient.